[Build] SPARK-2614: (2nd patch) Create a spark-XXX-examples.deb package in addition to the spark-XXX-all.deb (-Pdeb profile)

New patch that takes into consideration Mark Hamstra's suggestion (https://issues.apache.org/jira/browse/SPARK-2614) to create a separate (dedicated) spark_examples package (e.g spark-XXX-examples.deb) instead of bundleing the spark_examples.jar inside the spark-XXX-all.deb.

When build with the -Pdeb profile enabled the project creates two debian packages like this:
```
-rw-r--r--  1 tzoloc  720748206  108151256 Jul 27 23:27 spark_1.1.0-SNAPSHOT-2bbf2353_all.deb
-rw-r--r--  1 tzoloc  720748206   59732472 Jul 27 23:27 spark_1.1.0-SNAPSHOT-2bbf2353_examples.deb
```

 
@markhamstra here is the dependency on spark definition. 
I've rebased and and amended previous commit, which apparently has deleted the comment lines.